Indwelling ureteral stents are in common use today. These stents are placed in the ureter which is the duct between the kidney and the bladder, for establishing and/or maintaining an open patent flow of urine from the kidney to the bladder. The predominate indications for placing a ureteral stent include extrinsic compression, ureteral injury due to trauma, obstructive uropathy, and following surgery in the upper or lower urinary tract. Generally, the stent is comprised of a flexible material having sufficient resiliency to allow it to be straightened for insertion into the body passageway, while having sufficient memory to return to its predetermined retentive shape when in situ.
Indwelling ureteral stents are positioned in the ureter by various procedures including, antegrade (percutaneous) placement, retrograde (cystoscopic) placement through the urethra, as well as by open ureterotomy or surgical placement in the ureter under direct visual placement. Ureteral stent positioning may be accomplished by several methods. One method, a wire guide is introduced into the ureteral orifice in the bladder via a cystourethroscope under direct vision. A wire guide is advanced up the ureter until the advancing flexible tip of the guide is confirmed by x-ray or fluoroscopy to be in the renal pelvis of the kidney. A tubular stent with both ends open is fed into the exposed external segment of the wire guide and advanced over the wire guide by hand until a short segment of the stent is visible outside the cystourethroscope. A pusher catheter, "positioner" or length of the tubing is then fed into the exposed external end of the wire guide and advanced over the wire guide by hand until it abuts against the stent. With the wire guide held stationary, the positioner is advanced over the wire guide to push the tubular stent up the ureter to the renal pelvis. With the anatomical proximal end of the stent in the renal pelvis, positioner is held stationary while the wire guide is gradually extracted from the stent and the positioner. As the wire guide leaves the proximal end of the tubular stent, the retentive means of the proximal end of the stent is formed to retain the stent in the pelvis of the kidney. As the wire guide is withdrawn past the distal or intravesical, end of the stent, retentive hook or curve of the distal end is formed so that the stent is retained within the bladder. At this point, the positioner and wireguide are completely withdrawn leaving only the stent indwelling in the ureter, bladder and kidney.
In another method of ureteral stent placement, a ureteral stent having one tip closed is backloaded into the wire guide. In this "pushup" method, the tip of the wireguide contacts the closed tip of the ureteral stent, which is then introduced into the ureteral orifice in the bladder via a cystourethroscope under direct vision. The stent is advanced up the ureter under fluoroscopic control until the tip of the stent lies within the renal pelvis. A positioner catheter or length of tubing is fed into the external end of the wireguide and advanced over the wireguide by hand until it butts against the open, distal end of the stent. In yet another method, a single invasive entry into the ureteral orifice and ureter is disclosed in U.S. Pat. No. 4,957,479.
One of the problems with this procedure and the implantation of such ureteral stents is when sufficient pressure builds in the bladder, a back flow, or a reflux of urine may occur into the kidney. Where there is no infection or pyrogenic organism present, this is not a problem since the urine is generally considered a sterile fluid within the body. However, in the event of the presence of infection or pyrogenic organisms, possibility of reflux may result in the development of sepsis which is potentially lethal and generally, most prevalent in the elderly. The risk of sepsis increases with the employment of such urinary drainage stents and catheters, particularly in the ureter between the kidney and the bladder. In view of the foregoing, there is a need to provide a ureteral stent which will be beneficial in establishing and/or maintaining an open patent flow of urine from the kidney to the bladder while inhibiting the backflow or reflux of urine to the kidney.